Various types of vehicle braking systems are presently known. Most vehicles, particularly land vehicles, have drum or disc brakes in which the brake elements and friction surfaces are exposed to the atmosphere. Many land vehicles are subjected to excessive abrasive and corrosive material in the form of of liquid, dust, or the like. Particularly, off-highway vehicles such as those used at construction sites, in mines, quarries, and the like are subjected to environments which are much more detrimental to their braking system than highway vehicles. It has been found that the brakes of such vehicles rapidly wear and are often the subject of failure. To prevent such occurrences, there is a need in the art for a sealed brake for land vehicles intended for operation in such environments. To prolong the life of such a sealed brake and to reduce its operating temperature, it is most desirable that the same be a wet brake, filled with appropriate oil or other fluid.
It is also known in the art that brakes and clutches have generally similar structural and operational features. In such devices, and particularly those of the "disc" type, a single annular hydraulic or pneumatic piston may be employed for actuation of the unit. In such brakes and clutches, the piston is typically annular and is concentric with the clutch or brake assembly itself. However, annular pistons have limitations in size and often interfere with other brake or clutch elements. Accordingly, such devices are often made in such a manner as to employ multiple pistons, the same being uniformly radially and circumferentially spaced about the operational axis of the device. In such multiple piston devices, there is a need to have each piston communicate with the hydraulic or pneumatic pressure source. In the prior art, this has typically required an annular ring with two sealing elements or cross drilling from one piston cavity to the next, such an operation being both time consuming and difficult to perform.
There is presently a need in the art for a sealed multiple piston brake or clutch assembly in which all of the piston cavities are interconnected by a single oil passage and in which a single sealing element may be employed to seal that passage.